1. Field of the Invention
The invention generally relates to a lens, and more particularly to a fixed-focus lens.
2. Description of Related Art
With advances in optical-electronic technologies, an image apparatus such as digital video camera (DVC) and digital camera (DC) has been widely applied in daily life. Lens is one of main elements in the image apparatus, and configured to render images clearly on a screen or a charge coupled device (CCD). In case the image apparatus are applied in specific fields, a wide angle lens is adopted to increase a field of view (FOV). For instance, the wide angle lens is needed and adopted in a car back-up camera, a driving assistance camera, or a security surveillance camera. Generally, cameras for cars or the security surveillance camera are used in outdoor operations, thus, besides using of the wide angle lens, a certain degree of temperature tolerance is also required.
In U.S. Pat. Nos. 7,301,578, 7,869,141, 7,283,312, 7,023,628, US patent application No. 20120113532 and Japanese Patent No. 2007139985, different wide-angle lenses are respectively disclosed, and most of the wide-angle lenses utilize at least one set of cemented lens. Although the cemented lens is conducive in reducing an aberration and a chromatic aberration of the wide-angle lens, a cost thereof is relatively higher. Also, when operating in a high temperature environment, the cemented lens is not conducive in the outdoor operations due to risks in glue failure. Based on above, how to design a lens capable of maintaining in low manufacturing cost while providing high temperature tolerance is one of research focuses for the person skied in the art.